Interpretive Summary: It has been shown that Bos taurus × Bos indicus crossbred cows were exceptionally productive and efficient, especially in subtropical climates. However, as the proportion Bos indicus increased, the advantages of Bos indicus crosses were tempered by older age at puberty and temperament and reduced meat tenderness. Thus, one goal of the beef germplasm evaluation program has been to identify alternative tropically-adapted germplasm that minimizes or eliminates the detrimental traits of Bos indicus breeds. This experiment determined differences among beef breeds for carcass traits and ribeye steak eating quality by evaluating carcasses of steers produced by mating Angus and MARC III cows to bulls from six breeds including two tropically-adapted composite breeds of American origin (Brangus and Beefmaster), two tropically-adapted non-Bos indicus breeds (Bonsmara from South Africa and Romosinuano from Colombia) and compared them to Hereford and Angus. Thus, the objective was to compared alternative tropically-adapted breeds to tropically-adapted breeds commonly used in the U.S. Angus carcasses were similar in size, fatter, lower yielding, with more marbling and more tender LM compared to the American composite breeds. Bonsmara and Romosinuano breeds provide tropically-adapted germplasm with carcasses that are lighter, leaner, higher yielding, with similar marbling and LM that tended to be more tender than carcasses from the American composite breeds. These data provide producers with additional information when deciding which sire breeds will maximize profit potential in their production situation.

Technical Abstract:
The objective of this experiment was to evaluate alternative sources of tropically adapted germplasm and compare them to the Angus and Hereford sired crosses. Carcass, yield, and longissimus thoracis palatability traits from F1 steers (n = 621) obtained from mating Angus and MARC III cows to Hereford (H), Angus (A), Brangus (BR), Beefmaster (BF), Bonsmara (BO), or Romosinuano (RO) sires were compared. Data were adjusted to constant age (426 d), carcass weight (340 kg), fat thickness (1.0 cm), fat trim percentage (25%), and marbling (Small 00) end points. For Warner-Bratzler and slice shear force and trained and untrained sensory panel traits, data were obtained on LM from ribeye steaks stored at 2°C for 14 or 15 d postmortem. The following comparisons were from the age-constant end point. Carcasses from BF-, A-, and BR-sired steers (358, 355, and 351 kg, respectively) were heavier (P < 0.05) than carcasses from steers from H (343 kg) and BO (331 kg) sires, and RO-sired steers (318 kg) had the lightest (P < 0.05) carcasses. Adjusted fat thickness for carcasses from A- and BF-sired steers (1.3 and 1.2 cm, respectively) was higher (P < 0.05) than for carcasses from steers from BR (1.0 cm) and BO (0.9 cm) sires, and RO-sired steers (0.8 cm) had the lowest fat thickness. Longissimus areas were larger (P < 0.05) for carcasses from BO- and BR-sired steers (84.4 and 84.1 cm2, respectively) than for carcasses from BF- and H-sired steers (80.8 and 80.2 cm2). A greater (P < 0.05) percentage of carcasses from A-sired steers graded U.S. Choice (69%) than carcasses from other sire breeds (17 to 47%) except H (52%). Carcass yield of boneless, totally trimmed retail product was lowest (P < 0.05) for A-sired steers (60.1%) and highest (P < 0.05) for RO-, and BO-sired steers (64.4 to 63.5%). Considering all measurements LM from carcasses of A-sired steers tended to be more tender and LM from carcasses of BF-sired steers tended to be the least tender. American composite breeds BF and BR were heavier, fatter, lower yielding, with similar marbling scores but less tender LM than BO and RO. Angus carcasses were similar in size, fatter, lower yielding, with more marbling and more tender LM compared to the American composite breeds. Bonsmara and Romosinuano breeds provide tropically-adapted germplasm with carcasses that are lighter, leaner, higher yielding, with similar marbling and LM that tended to be more tender than carcasses from the American composite breeds.